Articles | Volume 10, issue 4
The Cryosphere, 10, 1631–1645, 2016
The Cryosphere, 10, 1631–1645, 2016

Research article 28 Jul 2016

Research article | 28 Jul 2016

Statistical indicators of Arctic sea-ice stability – prospects and limitations

Sebastian Bathiany1, Bregje van der Bolt1, Mark S. Williamson2, Timothy M. Lenton2, Marten Scheffer1, Egbert H. van Nes1, and Dirk Notz3 Sebastian Bathiany et al.
  • 1Department of Environmental Sciences, Wageningen University, 6708 PB Wageningen, the Netherlands
  • 2College of Life and Environmental Sciences, University of Exeter, Exeter, UK
  • 3Max-Planck-Institute for Meteorology, Bundesstrasse 53, 20146 Hamburg, Germany

Abstract. We examine the relationship between the mean and the variability of Arctic sea-ice coverage and volume in a large range of climates from globally ice-covered to globally ice-free conditions. Using a hierarchy of two column models and several comprehensive Earth system models, we consolidate the results of earlier studies and show that mechanisms found in simple models also dominate the interannual variability of Arctic sea ice in complex models. In contrast to predictions based on very idealised dynamical systems, we find a consistent and robust decrease of variance and autocorrelation of sea-ice volume before summer sea ice is lost. We attribute this to the fact that thinner ice can adjust more quickly to perturbations. Thereafter, the autocorrelation increases, mainly because it becomes dominated by the ocean water's large heat capacity when the ice-free season becomes longer. We show that these changes are robust to the nature and origin of climate variability in the models and do not depend on whether Arctic sea-ice loss occurs abruptly or irreversibly. We also show that our climate is changing too rapidly to detect reliable changes in autocorrelation of annual time series. Based on these results, the prospects of detecting statistical early warning signals before an abrupt sea-ice loss at a "tipping point" seem very limited. However, the robust relation between state and variability can be useful to build simple stochastic climate models and to make inferences about past and future sea-ice variability from only short observations or reconstructions.

Short summary
We examine if a potential "tipping point" in Arctic sea ice, causing abrupt and irreversible sea-ice loss, could be foreseen with statistical early warning signals. We assess this idea by using several models of different complexity. We find robust and consistent trends in variability that are not specific to the existence of a tipping point. While this makes an early warning impossible, it allows to estimate sea-ice variability from only short observational records or reconstructions.